A feed line switching apparatus or a feed line switching circuit which switches a connection relationship of a plurality of feed lines is used in, for example, an optical submarine branching apparatus used in a submarine cable system, and, when failure occurs in a feed line to the optical submarine branching apparatus, performs switching to another feed line.
For example, the optical submarine branching apparatus which switches a feed line in accordance with a command signal is called a remote control type submarine branching apparatus. Here, in the submarine cable system, building of a network including a plurality of branching apparatuses and terminal station apparatuses is required because of a request for a growing mesh of the network, reduction of construction cost, or the like. As the network becomes complex, control of the feed lines becomes difficult in a current-switching type branching apparatus and thus a remote control type submarine branching apparatus is used. In the remote control type submarine branching apparatus, the feed line can be switched in accordance with a command signal from the terminal station apparatus.
In conjunction with the feed line switching apparatus or the feed line switching circuit, a feed switching circuit of an undersea branching apparatus described in Patent Document 1 is configured such that, first, second, and third switching relays are arranged in first, second, and third branches of an electric path branched in three directions so that directions of operation currents are the same when viewed from its branching point, respectively, the first, second, and third switching relays have contacts for closing the second, third, and first electric branch paths normally and opening earth fault paths thereof normally, at least the earth fault path of the second branch is provided with a self-holding relay having a contact for self-holding the earth fault path, and the self-holding relay further has a normally open contact which is a path used to bypass a normally closed contact of the first branch.